Wet processing of silicon substrates is well known in the art. It is a process where substrates are treated with liquid agents, such as etchant chemicals or water, to etch selective portions of the substrate, remove photoresist, clean, and to perform other functions generally related to the fabrication of semiconductor devices.
Currently, the etchant chemicals are introduced to the substrates in one of two ways. The first way, known as batch processing, is to immerse a batch of substrates in a chemical bath for a specified period of time and removing them from the bath for rinsing. The second way, known as one-to-one processing, is to flood a single substrate with a wet chemical spray and to spin the substrate on a chuck. These two methods can be used in conjunction with each other. A typical wet processing of substrates entails a series of steps where the substrate is exposed to one type of chemical, then rinsed or dried, exposed to a different type of chemical (if needed), and so on, until the desired pattern is formed on the surface of the substrate.
Currently, the wet processing of substrates is not a completely controlled process for two main reasons. First, the substrates being processed are exposed to environmental factors which may cause undesirable effects on the final product. Because the substrate processing is done in an open environment, factors such as humidity, temperature, and contamination levels are not precisely controlled. Control over these factors is important because they affect the processing parameters and consequently the final outcome. For instance, humidity can affect how quickly an etchant evaporates from the surface of the substrate. If the evaporation occurs too quickly, there may not have been enough exposure to sufficiently etch the substrate.
To avoid these environment-related problems, the system must be in a closed environment. However, currently, the closed environment is generally only found in the dry-processing systems such as plasma etching or ion etching systems. And while the dry etching systems generally do not suffer from some of the shortcomings discussed above, they have other shortcomings not present in the wet processing such as lack of selectivity. Hence, dry-processing does not provide a complete solution.
The second reason for failure to achieve a controlled environment aside from the open environment is the inability to precisely control the amount of exposure the substrate has with a particular chemical. Excessive exposure may cause excessive removal of the substrate or photoresist. Under-exposure, on the other hand, may cause not enough removal. Controlling the amount of exposure to the various chemicals has been difficult because it is generally difficult to controllably remove the residual liquid from the surface of the substrate when the exposure is deemed to have been enough. This is particularly true for batch processing since the etchant chemical trickles over the edge of the substrate when the substrate is removed from the chemical bath. Although the one-to-one processing has attempted to solve this problem, the existing systems generally have not been completely successful.
These and other shortcomings have lead to slower processing time and/or performance defects that contribute to the general slow down in the overall manufacturing of semiconductor devices, and the lowering of yield. Although some wet processing systems with closed environment do exist, they have failed to achieve the level of etching uniformity that can be achieved via the present invention. As of this date, there has not been an apparatus or method of utilizing the selectivity of wet processing with the environmental controllability of dry etching while providing superior uniformity. Therefore, it is easy to see the desirability of having an apparatus and method for facilitating a controlled environment for a wet processing of wafer substrates.